1. Field of the Invention
This invention relates generally to continuous hot rolling bar mills, and is concerned in particular with a system and method for delivering the hot rolled products of such mills to a cooling bed.
2. Description of the Prior Art
In modern bar mills currently in operation, hot rolled bar products exit the last mill stand, and are subjected to cooling by being passed through one or more water boxes. The bar products are then subdivided into bar segments by a dividing shear, which includes a switching mechanism for alternately directing the bar segments to one or the other of two downstream delivery paths leading to the cooling bed. Pinch roll units, friction pads, or the like serve to decelerate the bar segments traveling along the delivery paths, with the result that the bar segments gradually slide to a halt before being laterally transferred onto the cooling bed.
Relatively high tonnage rates can be achieved with this type of arrangement when the mill is rolling larger product sizes, e.g., those having diameters above about 10.0 to 12.0 mm. These larger products have enough column strength to resist buckling as they are being pushed through the water boxes at relatively high mill delivery speeds on the order of 10 to 30 m/sec.
However, as product sizes decrease, so do their column strengths decrease, with the result that mill delivery speeds must be reduced in order to avoid buckling when pushing the smaller product sizes through the water boxes.
Thus, for example, a single strand mill rolling 8.0 mm rod for delivery to a laying head can operate at a delivery speed of 60 m/sec or greater, yielding a capacity of 85 tons/hour. However, a similar mill rolling 8.0 mm bar for delivery to a cooling bed must necessarily roll at a significantly reduced delivery speed of about 32 m/sec with a reduction in capacity to about 45 tons/hour. The reduced delivery speed for bar products is due in large part to the inability of conventional bar handling systems to bring faster moving products to a halt before they are transferred laterally onto the cooling bed.
An objective of the present invention is to increase the tonnage rate at which mills are able to roll bar products, in particular smaller product sizes, e.g., those having diameters smaller than about 12.0 mm.
A companion objective of the present invention is to raise the speed at which the smaller bar products are delivered from the mill, and to then decelerate such bar products before they are cooled in the water boxes prior to being delivered to the cooling bed.